Newbie

Set up to cut 4.5tpi on lathe correct gear and other settings; made scratch pass, perfect made second pass 1/2 thread off, 3rd pass back to 1st thread etc, grizz. book says use number 1 only[?] I wound up cutting leaving half nut engaged reversing back and got the thread cut but I would like to know what I did wrong. Neil

RGL

Set up to cut 4.5tpi on lathe correct gear and other settings; made scratch pass, perfect made second pass 1/2 thread off, 3rd pass back to 1st thread etc, grizz. book says use number 1 only[?] I wound up cutting leaving half nut engaged reversing back and got the thread cut but I would like to know what I did wrong. Neil

Active User

Check to see if your compound is at 29.5º or 60.5º. This is often the problem, the compound itself should be about 30º off from the axis of rotation, or the face of the chuck. Less than 45, not more than.

Brass

4.5 tpi wouldn't that be an odd numbered thread ?
I must admit when cutting metric threads, I leave the half nut engaged and wind back the chuck. But then again I run the lathe backwards and cut away from the chuck.

Just adding I don't bother with offseting the compound, I go straight in.

John York

4.5 tpi wouldn't that be an odd numbered thread ?
I must admit when cutting metric threads, I leave the half nut engaged and wind back the chuck. But then again I run the lathe backwards and cut away from the chuck.

Just adding I don't bother with offseting the compound, I go straight in.

4 1/2 TPI is our standard coarse for 2 1/4" diameter (in USA). As an aside, I understand that the Germans have the compound at parallel with the lathe's axis and go straight in and advance the compound towards the cut at each feeding in, this I was told by a German guy who worked in the shop where I apprenticed. I guess there is more than one way to skin a cat ------ For the thread dial, you should be able to use opposite numbers for half threads, quarter threads use one number only, according to info I have seen and my lathes work that way; usually it is even threads on any line or number, odd threads on numbers only, half threads on opposite numbers and quarter threads on one number only, and close anywhere on threads that are a factor of the lead screw, such as if you have a 4 thread screw, you can close anywhere on 2,4,8, 16, 32, etc.

Active User

What lathe are you using? I had a similar problem when learning to thread with my 10x22 and it came down to a spacer in the gear train that has to be changed, between metric threads ( normal turning operation ) and "standard " sae threads. The members here helped me thru it and I am certain will do the same now!

H-M Supporter - Gold Member

edit: delete "I would agree that something is loose." While it is possible, I don't think you would have returned to the proper setting on the third pass.

Since you were able to successfully cut the thread by leaving the half nuts engaged, I would conclude that the problem isn't in the gear train. That leaves the thread dial indicator. Possibilities include having a misaligned dial, the thread dial gear not fully engaged with the lead screw, or a loose thread dial gear. Your 4-1/2 tpi is a .222" pitch. Being off by one thread on the lead screw would shift the cut by .125" which is close to a half thread.

I had a problem with my Grizzly G0602 where the thread dial was not concentric with the thread dial axle and in some positions, it would the half nits would engage slightly off the mark. This would result in a similar situation as yours. I made a new thread dial which solved the problem.

Newbie

edit: delete "I would agree that something is loose." While it is possible, I don't think you would have returned to the proper setting on the third pass.

Since you were able to successfully cut the thread by leaving the half nuts engaged, I would conclude that the problem isn't in the gear train. That leaves the thread dial indicator. Possibilities include having a misaligned dial, the thread dial gear not fully engaged with the lead screw, or a loose thread dial gear. Your 4-1/2 tpi is a .222" pitch. Being off by one thread on the lead screw would shift the cut by .125" which is close to a half thread.

I had a problem with my Grizzly G0602 where the thread dial was not concentric with the thread dial axle and in some positions, it would the half nits would engage slightly off the mark. This would result in a similar situation as yours. I made a new thread dial which solved the problem.

I made about 6 lite passes using asharpie between passes trying to see what was wrong; it appeared to be a 2 start thread it measured 9tpi with thread gage but alternated threads each pass. I will check thread dial thanks for the input. like I said I cut the thread leaving the half nut engaged and backing out but it bugs me when I cant figure out why.

H-M Supporter - Gold Member

My Grizzly is a step down from yours. I have experienced the threading dial loosening off blues. Really cannot fathom how your threads could possibly shift on you when not disengaging on the return. I turned these threads on mine without a hiccup.

Attachments

Brass

I cut this today. 30 mm by 1.25 thread. Cut using my Myford lathe at 200 ish rpm.
Cutting away from the chuck and winding back by hand. There is only about 7 mm of thread.
The material 40 mm round mild steel bar. The hole is drilled 12 mm and then bored out to 1/2" inch.

Newbie

My Grizzly is a step down from yours. I have experienced the threading dial loosening off blues. Really cannot fathom how your threads could possibly shift on you when not disengaging on the return. I turned these threads on mine without a hiccup.